To accommodate weather observation and air surveillance requirements concurrently, the MPAR has been proposed as a solution. Since each function demands precise features, radar components are being upgraded to meet stringent requirements such as matched co-polarization patterns, highly-isolated dual polarization, and low cross-polarization level over the entire frequency bandwidth.
Dual linear-polarized antennas have been introduced as an appropriate solution to meet the aforementioned requirements and are undergoing significant developments. Microstrip patch antennas, owing to their low profile and ease of fabrication, make up a large percentage of such proposed dual-polarized antennas. Based on their feeding techniques, they can be categorized into different types: microstrip-fed, probe-fed, and aperture-coupled antennas. The highest isolation reported in microstrip-fed and probe-fed antennas is 30 dB. Feedline parasitic interference and stimulation of higher-order modes degrade the polarization purity in microstrip-fed and probe-fed antennas. Aperture-coupled antennas sacrifice some antenna features such as gain, simplicity, and low back lobe radiation to achieve a high level of isolation. Various aperture configurations have been suggested and up to 35 dB port-to-port isolation has been reported. To further enhance isolation and cross-polarization levels, differential feed methods have been studied. However, the implementation of two differential feeds in a single layer is challenging and it often results in gain loss, larger antenna area, or bulky multilayer structures.
Similar orthogonal structures such as cross dipoles and cross slots form another category. One proposed non-planar cross dipole provides 34 dB port-to-port isolation. However, due to a high sensitivity to fabrication tolerances, the antenna cross-polarization is severely degraded. In contrast, an easy-to-fabricate printed dipole with 35 dB port-to-port isolation was reported to suffer from collocation of co- and cross-polarization peaks in radiation pattern.
Thus the design of a dual-polarization antenna with high isolation between ports has always been a challenge to antenna designers. The novel antenna configurations of the present disclosure address the deficiencies of the previously proposed antenna designs.